What’s up, or what is “up”?
This usage of “up” is not spatial at all. It has a whole different meaning, although because we speak language mostly unconsciously, we would hard-pressed to tell a foreigner what this “up” meant. What it conveys is that the speaker has an intimate relationship with the location. One would not say “I was up at the dentist’s” — unless the dentist’s office was uptown, in which case you would intend “up” in its literal meaning. You would not say “I was up at that man Mr. Taylor’s” because, in referring to him as “that man,” you show that you don’t know him that well, such that his living space would not be one you thought of as a home away from home.
And if “up” is slang, then why, in other languages, when there is a similar way of conveying that same kind of meaning of intimate proximity, it’s treated as grammar? In Korean, “put” is a different word depending on how intimate the puttage is. You nohta a cup on the table, nehta an apple into a bowl and kkita a videocassette into its box. It’s a lot like the Ebonics “up”: In a way, you slide that videocassette all “up” into the box.
via nsfwish bol
